It is well known in the art to use magnetron plasma for etching or sputtering, which is implemented in production processes of electronic components such semiconductor devices.
Magnetron plasma is generated, as described below, using a magnetron plasma apparatus. A gas (e.g., halogen gas for etching and argon gas, etc. for sputter is introduced into a magnetron plasma apparatus, after which discharge is induced within the apparatus. Then, the electrons released due to the discharge serve to ionize the process gas within the apparatus, leading to the generation of secondary electrons. These secondary electrons collide with gas molecules with the result of promoting the ionization of the gas in the apparatus. The electrons and secondary electrons, which have been generated due to the discharge, acquire the forces generated by the magnetic and electric fields, and exhibiting drift movements.
The gas molecules are further ionized by the electrons exhibiting the drift movements, and new secondary electrons are generated due to the ionized gas molecules. Since the magnetron plasma apparatus repeats such processes and promotes gaseous ionization, it features that the ionization efficiency is very high. Therefore, the plasma generation using the magnetron plasma apparatus has the advantage that the efficiency thereof is two to three times that of a high-pressure discharge technology wherein no magnetic field is used.
One example of conventional magnetic field generator for magnetron plasma generation will be discussed with reference to FIGS. 29-32, and a conventional magnetron plasma etching apparatus will be discussed by referring to FIG. 33.
FIG. 29(a) is a schematic vertical cross sectional view of the plasma etching apparatus according to a first conventional example, and FIG. 29(b) schematically shows the motions of electrons within the apparatus of FIG. 29(a). As shown in FIG. 29(a), plate-like electrodes 10 and 12 are provided in parallel within the apparatus. A wafer (or workpiece) 16 is deposited on the electrode 10, which wafer is to be subject to etching treatment. The magnetic field generator 18 for generating magnetron plasma is provided on the plate-like electrode 12 (viz., provided at the opposite side of the other plate-like electrode 10).
The high-frequency voltage generator 19 is for generating alternating electric fields between the plate-like electrodes 10 and 12.
An arrow 20 in FIG. 29(a) indicates the direction of the electric field at the moment when the plate-like electrode 10 is negative and the plate-like electrode 12 is positive.
The conventional magnetic field generator 18 for magnetron plasma generation, which is illustrated in FIG. 29(a), comprises a ring-like permanent magnet 22, a disk-like permanent magnet 24 provided inside the ring of the magnet 22, and a yoke 26. The manner that the magnetic field generated by the magnetic field generator 18 reaches the wafer 16 by way of the electrode 12 is shown by magnetic force lines 28a and 28b. The lines of magnetic force 30 in FIG. 29(b) indicate in perspective the lines of magnetic force 28a and 28b shown in FIG. 29(a) on or above the surface of the wafer 16. As mentioned above, when the direction of the electric field is as indicated by the arrow 20, an electron 32 travels along endless track 34 while exhibiting the drift movement as shown in the drawing. Consequently, the electron(s) 32 is confined in the vicinity of the upper surface of the wafer 16, and hence the gaseous ionization is accelerated. For this reason, the apparatus shown in FIG. 29 is able to generate high-density of plasma.
However, among the magnetic force lines, those contributing to the electron drift movement are those perpendicular to the direction of electric field. That is to say, with the apparatus of FIG. 29, only the magnetic field component, which is in parallel with the surface of the wafer 16, is able to contribute to the electron drift movement.
In the magnetron etching apparatus, which uses the magnetic field generator for magnetron plasma generation according to the first conventional example shown in FIG. 29, a doughnut-like magnetic field is formed. As a result, the magnetic field strength in parallel with the surface of the wafer 16 varies extensively depending on the location as shown in FIG. 30.
Reference is made to FIG. 30, wherein the horizontal axis of the graph denotes the distance (r) from the center of the plasma zone (viz., the position immediately above the center point of the wafer 16) toward the circumference of the wafer, and wherein the vertical axis denotes the strength (H) of the magnetic field in parallel with the surface of the wafer 16. As mentioned above, as the horizontal magnetic field strength is larger, the density of puma produced is higher, and as such, the conventional example described with reference to FIG. 29 has encountered the problem that the wafer is partially etched. Further, the lack of uniformity of plasma results in potential distribution on the surface of the wafer (viz., results in charge-up), and consequently, leading to the fact that the elements formed on the wafer may be damaged.
In order to solve such a problem, it is vital to uniform the strength of the horizontal magnetic field over the largest possible range in the vicinity of the surface of the wafer 16. However, with the conventional apparatus shown in FIG. 29, it is not possible to address this difficulty.
In order to solve the above-mentioned problem, it is known in the art, as shown in FIG. 31, to make use of a dipole-ring magnet (denoted by reference numeral 35) which comprises a plurality of columnar anisotropic segment magnets arranged in the shape of ring. FIG. 31(a) is a top plan view showing the dipole-ring magnet 35, and FIG. 31(b) is a cross sectional view taken along a section line A-B of FIG. 31(a).
As shown in FIG. 31(a), the dipole-ring magnet 35 is configured such that a plurality of anisotropic segment magnets 40 are embedded in the base or support 42 of non-magnet material. As shown in FIG. 31(b), each of the plurality of segment magnets 40 is provided with a spacer 41 of non-magnetic material (for example, aluminum etc.) at the center in the lengthwise direction thereof in order to adjust the amount of magnetic flux.
The number of the anisotropic segment magnets 40 is eight or more, and is typically selected between eight(8) and thirty-two(32). In the particular case shown in FIG. 31, the number of magnets 40 is 16. The cross section of the anisotropic segment magnet 40 is arbitrary, and thus, the cross section may be circular, square, rectangular, trapezoidal, etc., and, the case illustrated in the drawing takes the form of rectangle. The arrows in the rings of the anisotropic segment magnets 40 respectively denote the directions of magnetization of the corresponding segment magnets. In the case where the segment magnets are arranged such that the directions of the magnetization thereof are as illustrated in FIG. 31(a), the magnetic field indicated by an arrow 43 is generated within the ring.
Inside the ring of the dipole-ring magnet 35, there are provided the plate-like electrodes 36 and 37 arranged in parallel with each other, and a wafer 38 is mounted on the plate-like electrode 37. As in the first prior art shown in FIG. 29, the high-frequency alternating electric field is generated between the plate-like electrodes 36 and 37 due to the high-frequency voltage applied to the plate-like electrodes 36 and 37. An arrow 44 indicates the direction of the electric field generated between the plate-like electrodes 36 and 37 at a certain time point High-density plasma is generated by the interaction between the electric field and the magnetic field.
When the dipole-ring magnet 35 is used with the magnetic field generator for magnetron plasma generation, it is necessary, as shown in FIG. 31(b), to generate the plasma formation space 46 near the central cross section C-D perpendicular to the lengthwise direction of the dipole-ring magnet 35.
This is because the magnetic field uniformity at the central cross section C-D normal to the lengthwise direction of the dipole-ring magnet 35 is better than the magnetic field uniformity near the lengthwise end of the magnet 35, and because at or in the vicinity of the central cross section C-D normal to the lengthwise direction of the magnet 35, the horizontal components of the lines of magnetic force are absolutely predominant which are very effective in order to confine the electrons above the surface of the wafer. For this reason, it is necessary to bring the plasma generation space 46 at or near the central section C-D perpendicular to the lengthwise direction of the dipole-ring magnet 35. That is to say, it is necessary, prior to entering into the etching process, to adjust the vertical location of the wafer 38 so that the space near the upper surface of the wafer 38 (viz., plasma formation space 46) must be brought to the central cross section C-D which is perpendicular to the lengthwise direction of the dipole-ring magnet 35.
FIG. 32 is a diagram schematically showing the magnetic field uniformity at the central cross section C-D perpendicular to the lengthwise direction of the dipole-ring magnet 35. In FIG. 32, the horizontal axis of the graph denotes the distance (r) from the center of the central cross section C-D toward the circumference thereof, and the vertical axis denotes the horizontal magnetic field strength (H). Character L indicates the radius of the plasma space 46. As understood from FIG. 32, the dipole-ring magnet is able to attain much better magnetic field uniformity than that of the first prior art (FIG. 30)(in other words, much flatter horizontal magnetic field strength can be realized).
In the following, in order to facilitate an understanding of the present invention, the outline of the known magnetron plasma etching apparatus will be described with reference to FIG. 33.
As shown in FIG. 33, the magnetron plasma etching apparatus is roughly divided into an etching chamber or room (A), a load lock chamber (C), and a cassette chamber (B), wherein the adjacent chambers are connected by way of a valve 49. One of a plurality of wafers 50 provided in the cassette chamber (B) is transferred into the etching chamber (A) using a conveyance arm 54 provided within the load lock chamber (C). The wafer, which is denoted by reference numeral 52 and which is transferred, using the conveyance arm 54, into the etching room (A), is placed on the plate-like electrode 56 in the etching chamber. Following this, the plate-like electrode 56 and the wafer 52 are lifted up to an etching position 60, which is denoted by a phantom line, by way of a lift 58.
Subsequently, etching is implemented by generating high-density plasma in the space in the vicinity of the upper surface of the wafer 52, which has been placed at the etching position, by way of the interaction between the electric field generated between the plate-like electrodes 56 and 62 and the magnetic field generated by the magnetic field generator (viz., dipole-ring magnet 64). When implementing the etching, a process gas is introduced into through a gas induction pipe 66 and discharged from a gas exhaust pipe 68. In addition, the gas exhaust pipe 68 is also connected to the cassette chamber (B) and the load lock chamber (C) in order to discharge the process gas which flows thereinto when the valve 49 is opened.
As mentioned above, after the wafer is transferred into the reaction room (processing room) such as the etching chamber, it is necessary to raise, using a lift, the position in the vicinity of the top surface of the wafer up to the best location wherein the best magnetic field uniformity is present at the center portion of the dipole-ring magnet. Furthermore, after the wafer has been processed, the wafer should be lowered, using the lift, to a wafer taking-out position which is the same as that of the wafer carrying-in position). Therefore, in order to decease the size of the magnetron plasma apparatus, simplify the structure thereof, and prevent the generation of dust from the lift mechanism, it is highly desirable to shorten the wafer's vertical travel distance within the etching chamber as much as possible. Furthermore, it is quite desirable if it is able to render it unnecessary to vertically transfer the wafer itself.
By the way, as mentioned above, the etch uniformity can be improved to some extent by using the dipole-ring magnet. However, it became clear that the etch uniformity varies depending on the film material to be etched. More specifically, the prior art suffers from the difficulties that the uniformity of etching varies in the radial direction of the wafer, and the etching profile becomes uneven in the diameter direction of the wafer. The inventors of the instant patent application have made extensive efforts to overcome the aforesaid problems, and concluded that it is possible to further improve the etch uniform if the incidence angle of the magnetic force line to the wafer surface is controlled while changing no magnetic field strength. The just-mentioned phrase “the incidence angle of the magnetic force line to the wafer surface is controlled” implies that the direction of the magnetic field relative to the wafer surface on which the etching is to be implemented is controlled. By using this control, it became clear that the etch uniformity is markedly improved. The inventors has noticed that it is possible to effectively control the etch uniformity by changing the angle of the magnetic field (viz., line of magnetic force) to the wafer surface, and further noticed that there exists an optimum angle(s) according to the conditions relating to an etching gas(es) and the kinds of films to be etched
It is therefore an object of the present invention to provide a magnetic field generator for magnetron plasma generation wherein the direction of the magnetic field to a wafer surface (viz., the direction of the magnetic field in the vicinity of the wafer surface to be etched) can be controlled so as to attain the etch uniformity.
Another object of the present invention is to provide an etching apparatus or system and method, all of which utilize the above-mentioned magnetic field generator for magnetron plasma generation.